Abstract

The evolution of communication requires changes in both signals and the criteria used by receivers to select signals. The question arises: Do changes occur first in signals, first in receivers, or are tight co‐evolutionary changes required in both signals and receivers? In the gray treefrog complex, spectral properties of calls are conserved: in both the diploid ancestral species (Hyla chrysoscelis) and in derived, tetraploid lineages (nominally, H. versicolor) there are two spectral peaks: a dominant band centered at about 2.4 kHz, and a secondary band (−8 to −10 dB) at about 1.2 kHz. Whereas females of the ancestral species have a weak preference for calls consisting only of the secondary band to calls having only the dominant band, females of the derived species strongly prefer calls with just the dominant band. Thus, an evolutionary change in preference has preceded any change in the spectral properties of the call. Temporal differences between the species include pulse rate, pulse duration, and pulse shape. Whereas females of the ancestral species use pulse rate alone for call discrimination, females of the derived species base preferences on all three properties, thus suggesting a co‐evolutionary change. [Work supported by NSF and NIMH.]